The human league: what separates us from other animals?


You are an animal, but a very special one. Mostly bald, you’re an ape, descended from apes; your features and actions are carved or winnowed by natural selection. But what a special simian you are. Shakespeare crystallised this thought a good 250 years before Charles Darwin positioned us as a creature at the end of the slightest of twigs on a single, bewildering family tree that encompasses 4bn years, a lot of twists and turns, and 1 billion species.


“What a piece of work is a man!” marvels Hamlet. “How noble in reason! How infinite in faculty! … In action how like an angel! / In apprehension how like a god! … The paragon of animals!” Hamlet then ponders the paradox at the heart of humankind: what is this quintessence of dust? We are special, but we are also merely matter. We are animals, yet we behave like gods. Darwin riffed on Hamlet in 1871 in his second masterpiece, The Descent of Man, declaring that we have “god-like intellect”, yet we cannot deny that man – and woman – carries the “indelible stamp of his lowly origin”. This is the central question in understanding our place in the scheme of evolution.


What makes us special, while we remain rooted in nature? We evolved from earlier creatures, each on a unique trajectory through time. We share DNA with all the organisms that have ever existed; the proteins our genes encrypt utilise a code that is indistinguishable from that in an amoeba or a zebu.


 Only 0.1% of the 900,000,000 acts of heterosexual intercourse taking place each year in Britain results in a fertilised egg

How did we become the beings that we are today? Scientists call this state “behavioural modernity”, or sometimes “the full package”, meaning all the things that we consider as part of the human condition: speech, language, consciousness, tool use, art, music, material culture, commerce, agriculture, non‑reproductive sex and more. Precisely when these facets of our lives today arose in our species is debated. But we do know that within the last 40,000 years, they were all in place, all over the world. Which facet singles us out, among other animals – which is distinctively human?



Navigating this territory can be treacherous, and riven with contradictions. We know we are animals, evolved via the same mechanisms as all life. This is comprehensively displayed in the limitless evidence of shared evolutionary histories – the fact that all living things are encoded by DNA. Or that similar genes have similar functions in distantly related creatures (the gene that defines an eye is virtually the same in all organisms that have any form of vision). Or that our bodies harbour the indelible stamps of common descent in our bones (our hands contain bones almost perfectly like-for-like with the bones in the flat paddle of a dolphin’s fin, and with a horse’s front legs, and a bat’s wings).


Prudent scepticism is required when we compare ourselves with other beasts. Evolution accounts for all life but not all traits are adaptations. We use animals in science every day to try to understand complex biochemical pathways in order that we might develop drugs or understand disease. Mice, rats, monkeys, even cats, newts and armadillos, provide invaluable insights into our own biochemistry, but even so, all researchers acknowledge the limitations of those molecular analogies; we shared ancestors with those beasts millions of years ago, and our evolutionary trajectories have nudged that biochemistry to suit each species as it is today.


A chimpanzee will use a stick to winkle out a grub from the bark of a tree – Caledonian crows have the same ability

A chimpanzee can use a stick to winkle out a grub from the bark of a tree – Caledonian crows have the same ability. Photograph: David Samson/PA

When it comes to behaviour, though, the parallels frequently become distant, or examples of convergent evolution. The fact that a chimpanzee uses a stick to winkle out a fat grub from the bark of a tree is a trick independent of the same ability in Caledonian crows, whose skills are frequently the source of increasing wonder as we study them more. Humans are obligate tool users; we’ve extended our reach far beyond our grasp by utilising nature and inventing technology. But many other creatures use tools, around 1% of all animals, and these span nine classes – sea urchins, insects, spiders, crabs, snails, octopuses, fish, birds and mammals. What this inevitably means is that using tools is a trick that has been acquired many times in evolution, and it is virtually impossible to assume a single evolutionary antecedent from which this behaviour sprang. Orangutans use leaves and branches as gloves when handling spiny fruit and as hats when it’s raining, and they fashion twigs to aid masturbation. Chimps sharpen sticks with their teeth with which to kebab sleeping bush babies. Boxer crabs carry pairs of stinging anemones to ward off enemies, which earns them the less hardcore nickname of “pom-pom crabs”. There is no evidence that these similar behaviours show continuity through time.


 Animal behaviour shows that homosexuality – in many places still decried as a crime against nature – is widespread

Arguments around these issues are generally the preserve of scientists. But there is a set of behaviours that are also inspected forensically and with evolution in mind whose reach extends far beyond the academy. We are a species that devotes enormous resources, effort and time to touching each other’s genitals. Most animals are sexual beings and the primary function of sex is to reproduce. The statistician David Spiegelhalter estimates that up to 900,000,000 acts of human heterosexual intercourse take place per year in Britain alone – roughly 100,000 per hour. Around 770,000 babies are born in Britain each year, and if we include miscarriages and abortions, the number of conceptions rises to about 900,000 per year.



What that means is that of those 900,000,000 British encounters, 0.1% result in a fertilised egg. Out of every 1,000 sexual acts that could result in a baby, only one actually does. In statistics, this is classed as not very significant. If we include homosexual behaviour, and sexual behaviour that cannot result in a pregnancy, including solitary acts, then the volume of sex that we enjoy magnificently dwarfs its primary purpose.


Is Homo sapiens the only species that has decoupled sex from reproduction? Enjoying sex might seem like a uniquely human experience, yet while we are reluctant to consider pleasure in other animals, we are certainly not the only animals that engage in non-reproductive sex. Zoo behaviour is often weird, as animals in captivity are far from their natural environment, but there are two male bears in Zagreb zoo who enjoy a daily act of fellatio, while simultaneously humming. Some goats perform auto‑fellatio (which, according to the famous Kinsey Report on sexual behaviours, 2.7% of men have successfully attempted). Males of some 80 species, and females of around 50 species of primates are frequent masturbators. Some behaviours reflect deviant or criminal sexual behaviours, such as sea otters who drown females and then keep their bodies to copulate with. The award for sheer ingenuity goes to the dolphins: there is one reported case of a male masturbating by wrapping an electric eel around his penis.



Some – not all – of these seemingly familiar sexual practices can be explained readily. Male Cape ground squirrels are promiscuous, and masturbate after copulation, we think, for hygiene reasons, protecting themselves from sexually transmitted diseases by flushing their tubes. Other behaviour is still mysterious to us: giraffes spend most of their time sexually segregated, and the vast majority of sexual relations appear to be male-to-male penetration. As with the myriad examples of sexual behaviour between members of the same sex, it demonstrates that homosexuality – once, and in many places to this day, decried as a crime against nature – is widespread.



Because sex and gender politics are so prominent in our lives, some look to evolution for answers to hard questions about the dynamics between men and women, and the social structures that cause us so much ire. Evolutionary psychologists strain to explain our behaviour today by speculating that it relates to an adaptation to Pleistocene life. Frequently these claims are absurd, such as “women wear blusher on their cheeks because it attracts men by reminding them of ripe fruit”.


Purveyors of this kind of pseudoscience are plenty, and most prominent of the contemporary bunch is the clinical psychologist and guru Jordan Peterson, who in lectures asserts this “fact” about blusher and fruit with absolute certainty. Briefly, issues with that idea are pretty straightforward: most fruit is not red; most skin tones are not white; and crucially, the test for evolutionary success is increased reproductive success. Do we have the slightest blip of data that suggests that women who wear blusher have more children than those who don’t? No, we do not.


Peterson is also well known for using the existence of patriarchal dominance hierarchies in a non-specific lobster species as supporting evidence for the natural existence of male hierarchies in humans. Why out of all creation choose the lobster? Because it fits with Peterson’s preconceived political narrative. Unfortunately, it’s a crazily poor choice, and woefully researched. Peterson asserts that, as with humans, lobsters have nervous systems that “run on serotonin” – a phrase that carries virtually no scientific meaning – and that as a result “it’s inevitable that there will be continuity in the way that animals and human beings organise their structures”. Lobsters do have serotonin-based reward systems in their nervous systems that in some way correlate with social hierarchies: higher levels of serotonin relate to increased aggression in males, which is part of establishing mate choice when, as Peterson says, “the most desirable females line up and vie for your attention”.


Killer whales, here entering a bay of King Penguins on sub-Antarctic Marion Island, live in a matriarchal social group.

Killer whales, here entering a bay of King Penguins on sub-Antarctic Marion Island, live in a matriarchal social group. Photograph: Nico de Bruyn/PA

Sexual selection is one of the driving forces of natural selection in most animals. In general, males compete with each other, and females subsequently have choice over which males they mate with. While this is one of the most studied areas of evolutionary biology, it’s incredibly hard to establish that rules that apply to lobsters (or does and stags, or peacocks and peahens) also apply to humans. There are physical and behavioural differences between men and women in relation to sex, but our cultural evolution has loosened the shackles of natural selection to the extent that we cannot satisfactorily match our behaviour with other beasts, and claims that we can are often poor science.


Peterson believes that the system that is used by lobsters is why social hierarchies exist in humans. The problem with the assertion is this: serotonin is indeed a major part of the neural transmitter network in humans, but the effect of serotonin in relation to aggression is the opposite. Lower levels increase aggression, because it restricts communication between the frontal cortex and amygdala. Lobsters don’t have an amygdala or frontal lobes. Or brains for that matter. Most serotonin in humans is produced to aid digestion. And lobsters also urinate out of their faces. Trying to establish evolutionary precedents that justify or explain away our own behaviour is scientific folly.


 What humans uniquely do is that we accumulate culture, and build on it. Many animals learn, but only we teach

If you wanted to make a different but equally specious political argument with a waft of science about how to arrange our society, you could compare us to killer whales. They live in a matriarchal social group, in some cases led by post-menopausal females. Or hyenas, the animal with the greatest jaw strength of any, which are also matriarchal, and engage in clitoral licking, to bond socially and to establish hierarchy. Or the insect order hymenoptera, which includes ants, bees and wasps, and are roughly the same evolutionary distance from us as lobsters. Their social hierarchy involves a single queen and males, whose role is twofold: protecting the colony, and providing sperm on demand – they are literally sex slaves. Or the freshwater small invertebrates called bdelloid rotifers: millions of years ago they abandoned males altogether, and seem to be doing just fine.


Yes, hierarchies assuredly exist in animals as competition is an inherent part of nature, and our sexual biology has common roots with all life on Earth. But we should not presume that understanding the biology of other animals will necessarily illuminate our own, as Peterson does. It’s a strange irony that someone who claims to bow to evolution should simultaneously fail to grasp its concepts. In some ways it’s a less cogent argument to an evolutionary biologist than that of creationists, who simply deny that evolution has happened. Then again, it was Darwin who said that “ignorance more frequently begets confidence than does knowledge”. Nowadays, you can buy “lobster dominance” T-shirts.


A peacock's tail: how Darwin arrived at his theory of sexual selection

We crave stories, and for those tales to deliver narrative satisfaction. We want dramatic triggers that bestow us with behaviours that are ours alone and therefore might be used to define humankind, and in doing so give us a sense of belonging or even purpose in the confusing modern world. We look to science and history to fulfil those cravings. But life is complex, culture is dynamic: evolution doesn’t work that way. Sometimes we talk about cultural evolution in opposition to biological evolution, the former being passed on socially, the latter being encoded in our DNA. But the truth is that they are intrinsically linked, and a better way to think about it is as gene-culture co-evolution. Each drives the other, and cultural transmission of ideas and skills requires a biologically encoded ability to do so. Biology enables culture, culture changes biology. What humans uniquely do is that we accumulate culture, and build on it. Many animals learn, but only we teach.


As we meandered into the most recent 100,000 years or so, our culture became ever more significant in crafting our abilities. This is apparent in the fact that our bodies have not significantly changed in that time. A woman or man from 1,000 centuries ago would fit in perfectly well in any city in the world today if we tidied them up and gave them a haircut. But the way we live our lives since then has become ever more complex.


We are desperate to find the things that tip us over the edge from being merely an animal into Hamlet’s paragon of animals. Was it our language? Was it religion, or music, or art, or any number of things that are not as unique to us as we had once thought? The truth is that it was all of these things and more, but crucially, it was in the engagement of our minds to transmit skills and ideas to others. We changed our societies and maximised how culture is transmitted. We took evolution’s work, and by teaching each other, we created ourselves. The stories we tell about how we came to be who we are often neglect the complexity of biology and the oceans of time during which we evolved. To understand human evolution, we need new stories.

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